The present invention relates to a cutting mechanism used in a thermal-shrinking film labeling machine and controlled to cut a thermal-shrinking film, and more particularly to such a cutting mechanism which uses compressed air (hydraulic oil) to turn a set of cutting tool assemblies back and forth in cutting a tubular thermal-shrinking film at a cylindrical shaft.
Various thermal-shrinking film labeling machines have been disclosed for use in fastening a printed thermal-shrinking film to commercial products. These thermal-shrinking film labeling machines commonly have a cutting mechanism controlled to cut off the thermal-shrinking film. FIG. 1 shows a cutting mechanism for a thermal-shrinking film labeling machine according to the prior art in which a wheel A2 is revolvably mounted around a shaft A1, and a tool holder A3 is revolvably supported on the wheel A2 to hold a cutting blade A4. When the wheel A2 is turned by a belt transmission mechanism (not shown), the tool holder A3 is simultaneously turned, causing the cutting blade A4 to cut a tubular thermal-shrinking film (not shown) at along an annular groove A5 of the cylindrical shaft A1. This structure of cutting mechanism has a complicated structure. Further, when the wheel A2 is turned through one run, the cutting blade A4 must be returned to their former positions for a next cutting operation. Therefore, this structure of cutting mechanism is not efficient in use. FIG. 2 shows another structure of cutting mechanism for a thermal-shrinking film labeling machine according to the prior art, in which a wheel B2 is revolvably mounted around a shaft B1, a cutting tool assembly B4 is pivoted to the wheel B2 to hold a cutting blade B7, a spring device B3 is coupled between the wheel B2 and the cutting tool assembly B4, a first push block B5 adapted to push the cutting tool assembly B4 into the cutting position, and a second push block B6 adapted to push the spring device B3 in returning the cutting tool assembly B4. This structure of cutting mechanism is still complicated and not efficient in use. FIG. 3 shows still another structure of cutting mechanism for a thermal-shrinking film labeling machine according to the prior art, in which a plurality of cutting tool assemblies C2 are arranged around a center shaft C1 to hold a respective cutting blade C3 and turned by a motor C5 through toothed belts C6;C7. When the cutting tool assemblies C2 are turned, the cutting blades C3 are moved over an annular groove C4 around the periphery of the center shaft C1 to cut a thermal-shrinking film. After each cutting operation, the cutting tool assemblies must be synchronously turned through 360.degree. and then retained in position for a next cutting operation. Because the effective cutting angle of the cutting blade of each cutting tool assembly is within 180.degree., much time is wasted in returning the cutting tool assemblies after each cutting operation. FIG. 4 shows still another structure of cutting mechanism for a thermal-shrinking film labeling machine according to the prior art, in which four links D2 are pivotably arranged around a center shaft D1 to hold a respective cutting blade D3 at one end and a respective roller D5 at an opposite end, and a cam D4 is turned to move the rollers D5 of the links D2, causing the cutting blades D4 to be moved back and forth relative to the periphery of the center shaft D1 in cutting a tubular thermal-shrinking film. Further, each cutting blade D3 is mounted on a respective dovetail block that can be adjusted in a dovetail groove and then fixed at the desired locating to fit the diameter of the tubular thermal-shrinking film to be cut. This structure of cutting mechanism is still complicated. Furthermore, the applicable position adjusting range of the cutting blade D3 is limited. Therefore, this structure of cutting mechanism is not suitable for cutting tubular thermal-shrinking films having a great difference in diameter.